This invention relates to turbine vane assemblies, for example of the type used in gas turbine engines. More particularly in one embodiment, it relates to a turbine vane assembly including at least one low ductility vane carried at least in part by a compliant seal to enable expansion and contraction of the vane independently from at least one of spaced apart metal supports or bands.
Components in sections of gas turbine engines operating at elevated temperatures in a strenuous, oxidizing type of gas flow environment typically are made of high temperature superalloys such as those based on at least one of Fe, Co, and Ni. In order to resist degradation of the metal alloy of such components, it has been common practice to provide such components with a combination of fluid or air cooling and surface environmental protection or coating, of various widely reported types and combinations.
One type of such a gas turbine engine component is a turbine stator vane assembly used as a turbine section nozzle downstream of a turbine engine combustion section. Generally, such assembly is made of a plurality of metal alloy segments each including a plurality of airfoil shaped hollow air cooled metal alloy vanes, for example two to four vanes, bonded, such as by welding or brazing, to spaced apart metal alloy inner and outer bands. The segments are assembled circumferentially into a stator nozzle assembly. One type of such gas turbine engine nozzle assembly is shown and described in U.S. Pat. No. 5,343,694xe2x80x94Toberg et al. (patented Sep. 6, 1994).
From evaluation of service operated turbine nozzles made of coated high temperature superalloys, it has been observed that the strenuous, high temperature, erosive and corrosive conditions existing in the engine flow path downstream of a gas turbine engine combustion section can result in degradation of the environmental resistant coating and/or alloy substrate structure of vanes of the nozzle. Repair or replacement of one or more of the vanes has been required prior to returning such a component to service operation. Provision of turbine vanes of adequate strength and more resistant to such degradation would extend component life and time between necessary repairs, decreasing cost of operation of such an engine.
In one form, the present invention provides a turbine vane assembly comprising an outer vane support, an inner vane support in a fixed spaced apart position from the outer vane support, and at least one airfoil shaped vane supported between the outer and inner vane supports. The vane is of a low ductility material, for example based on a ceramic matrix composite or an intermetallic material, having a room temperature ductility no greater than about 1%. The outer and inner vane supports are of material having a room temperature ductility of at least about 5%. A high temperature resistant compliant seal is disposed between the vane and at least one of the vane supports, substantially sealing the vane from passage of fluid between the vane and the vane support, enabling the vane to expand and contract independently of the vane support. In one form, the vane supports are of a high temperature metal alloy, for example based on at least one of Fe, Co, and Ni, having a room temperature tensile ductility in the range of about 5-15%.